Process for the production of cylindrical hollow bodies in the centrifugal casting process

ABSTRACT

PROCESS FOR THE PRODUCTION OF CYLINDRICAL HOLLOW BODIES WITH A PEARLITIC STRUCTURE FROM CAST IRON MATERIAL BY SUPERHEATING A EUTECTIC OR HYPEREUTECTIC MELT AFTER ADDING ALLOYING ELEMENTS SO THAT IN SUBSEQUENT CASTING A MIXTURE SUPERSATURATED WITH CARBON RESULTS, AND THE PRODUCTS THEREOF.

United States Patent Office 3,695,865 Patented Oct. 3, 1972 US. Cl.75-430 R 8 Claims ABSTRACT OF THE DISCLOSURE Process for the productionof cylindrical hollow bodies with a pearlitic structure from cast ironmaterial by superheating a eutectic or hyperentectic melt after addingalloying elements so that in subsequent casting a mixture supersaturatedwith carbon results, and the products thereof.

The invention relates to a process for the production of cylindricalhollow bodies, especially cylinder liners, in the centrifugal castingprocess from cast iron material with at least 3% by weight of graphiteand 3.7% by weight of total carbon content. I

The production of cylindrical hollow bod1es, for example cylinderliners, with a pearlitic structure and a total carbon content of up toabout 3.7% by weight in the centrifugal casting process is alreadyknown. Whilst the pearlitic structure favourably influences the wearproperties, the graphite serves the purpose of creating anti-frictionproperties (Notlaufeigenschaften) which are necessary in the case ofinsufficient separate lubrication. In these known cylindrical hollowbodies the graphite content in the structure amounts to a maximum of2.8%, since up to 1% of carbon in pearlite is bound as cementite.

Until now, it has not been possible in the centrifugal casting processto treat a pearlitic cast iron with graphite content of more than 2.8%by weight, since the structure such high carbon content in relation tothe silicon content is either ferrite or carbide.

The problem underlying the invention resides in the creation of aprocess, according to which cylindrical hollow bodies, for examplecylinder liners, axials and bearing rings, can be produced which aredistinguished particularly by improved anti-friction characteristics andby a higher corrosion resistance against acid combustion products andcooling water.

The process according to the invention for the production of cylindricalhollow bodies, more especially cylinder liners, is characterised in thata eutectic or hypereutectic melt, after the addition of such alloyingelements which are required for the formation of a pearlitic structure,is superheated in a melting furnace and so far carburised, that in thesubsequent tapping and casting, limited through temperature drop andinoculation, a mixture supersaturated with carbon results, which undercontrolled rotation conditions is cast in such a way, that the soproduced cylindrical hollow body has at its bearing surface at least 3%by weight of graphite in a pure pearlitic structure.

This has essentially the advantage, that in the so produced cylindricalhollow bodies, which are stressed by friction and the separatelubrication of which is not unconditionally assured, the bearing surfacehas significant surface portions of graphite, so that adequate resultingproperties are thus assured with high stress. Thereby, the bearingsurface of these liners contains about 19% graphite. This signifies incontrast to the usual pearlite casting in which only about 12% of thesurface consists of graphite, a relative increase of the graphitesurface of about 50%.

Suitably a eutectic to hypereutectic cast iron with the followinganalysis is used:

Percent Carbon 23.7 Silicon (max.) 1.5 Manganese (max) 1.0 Phosphorus(max.) 1.0 Chromium (max.) 0.9 Molybdenum (max.) 0.9 Nickel (max) 2.5Copper (max.) 1.5 Tin (max.) 1.2 Sulphur (max.) 0.12

Thereby a heterogeneous mixture of liquid cast iron and containing solidgraphite can be teemed into the centrifugal mould.

The carbon supersaturation and graphite separation can also be initiatedthrough mould inoculation only in the centrifugal mould. Advantageouslythe peripheral speed of the centrifugal mould amounts to a maximum of 5metres per second.

This has essentially the advantage that on the one hand zone formationis avoided or reduced and on the other hand a coarser graphite isobtained and a fine eutectic graphite is avoided.

If desired and a fine eutectic graphite formation is to be obtained, theperipheral speed can amount to over 5 metres per second.

For production of cylindrical hollow bodies with variable graphitecontent in the bore, the melt is suitably cast to liners with diiferentexternal diameters of constant bore. Accordingly, there then resultshigh machining allowances or high wall thicknesses respectively of highgraphite content in the bore and visa versa.

Further advantages are shown from the following explanation ofembodiments of the invention:

A hypereutectic cast iron is used, which is melted and superheated in anelectric furnace and is highly carburised. In the filling in the castingladle through inoculation and assisted through temperature drop aheterogeneous mixture, supersaturated with carbon, from liquid cast ironand graphite results. By flotation the graphite is enriched in thedirection of the bore and there is then obtained according to thisprocess, for example at the bearing surface of the cylinder liner, notonly absolute high graphite content, but increased graphite content inrelation to the external surface of the liner. The graphite contentattainable in the bore increases, with equal chemical analysis of themelt, with increasing wall thickness of the unfinished piece inconsequence of the flotation process taking place.

Example Raw material 116 X X70 96 X70 Wall thickness, millimeters- 23 1813 C (furnace), percent 4. 6 4. 6 4. 6 Graphite, percent 3. 9 3. 4 3. 18(Bearing surface), combined carbon, percent 1. 0 0. 86 0. 96 Silicon(furnace), percent. 1. 05 1.05 1. O5 Silicon (ladle), percent.-. 1.26 1. 30 1. 26 Mn, percent. 0. 29 0. 47 0. 29 P, percent 0. 12 0. 34 0.12 8, percent. 0. 038 0. 04 0. 038 Or, percent.. 0.07 0. 30 0. 07 N 1,percent Traces 0.27 Traces Mo, percent Traces O. 25 Traces Sn, percent0. 5

The cylinder liners produced according to the process of the inventionhave, even with small wall thicknesses of for example, 10 to 25 mm.,still have several zones of variable structure. In the processing of thebearing surface guided difierent zones are chamfered the graphitecontents of which differ up to 1%. The number of these zones can, inaccordance with the invention, be reduced to a maximum of two and inparticular a graphite-rich inner zone and a graphite-poor outer zone. Itis possible even to attain a continuous graphite enrichment in thedirection of the axis of rotation. In order to avoid more than twodifferent zones the peripheral speed of the rotating liners is adjustedin relation to the central diameter of a blank to a maximum of 5 metresper second. This permits the use both of a eutectic and hypereutecticmelt with at least 3.7% carbon which for the rest has the Supplementaryinoculants The carbon supersaturation accordingly occurs during thesolidification of the melt. The graphite present after the casting thenfloats in the direction of the bore up to completion of thesolidification so that the latter is thus enriched with graphite. Anexclusive as well as additional graphite separation can be obtainedthrough mould inoculation.

The liners produced in accordance with the invention have in the purepearlitic structure a microhardness of 220 to 290 HV. The selectedregulation of the peripheral speed influences both the formation of theindividual zones and the graphite formation. Accordingly, lowerperipheral speeds of a maximum of 5 metres per second yield coarsegraphite and higher peripheral speeds of more than 5 metres per secondfine to punctiform graphite of dendritic formation.

I claim:

1. Process for the production of cylindrical hollow bodies, particularlycylinder liners in the centrifugal casting process from a cast ironmaterial with at least 3.7% by Weight total carbon content, whichcomprises superheating from a eutectic to a hypereutectic highlycarburised melt in the furnace after the addition of the alloyingelements required for the formation of a pearlitic structure, so thatsubsequently in the casting ladle through inoculation and through atemperature drop a mixture supersaturated with carbon results, whichmixture under controlled rotation conditions is cast in such a way, thatthe so produced cylindrical hollow body has at its bearing surface atleast 3% by weight of graphite in a pure pearlitic structure.

2. Process according to claim 1, wherein eutectic to hypereutectic meltis cast iron with the following analysis is used:

3. Process according to claim 1, wherein a heterogeneous mixture fromliquid cast iron containing solid graphite is teemed into a centrifugalmould.

4. Process according to claim 1, wherein the carbon supersaturation andgraphite separation is initiated by mould inoculation in the centrifugalmould.

5. Process according to claim 1, wherein the peripheral speed of thecentrifugal mould amounts to a maximum of 5 metres per second.

6. Process according to claim 1, wherein the peripheral speed of thecentrifugal mould amounts to more than 5 metres per second.

7. Process according to claim 1, wherein the melt is cast to liners withdifferent external diameters of constant bore.

8. The process of claim 1, wherein said melt is a hypereutectic highlycarburised cast iron.

References Cited UNITED STATES PATENTS 1,280,418 10/1918 DeLavaud 148-35X 1,614,863 1/ 1927 Beatty 14 8-35 1,702,128 2/1929 Niedringhaus 148-351,871,544 8/ 1932 McCarroll 148-35 X 1,953,180 4/ 1934 Langenberg148--35 X 1,971,385 8/1934 Russell 148-35 X 2,689,990 9/1954 Samuels148-35 X 3,559,775 2/1971 Miller 148-35 X 1,793,268 2/ 1931 Williams -582,731,690 1/1956 Coupland, Jr., et al. 1641 14 X 3,415,307 12/1968 Schuhet al 164-114- 3,563,300 2/1971 Honda et al. 164-414 X L. DEWAYNERUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner US. Cl. X.R.

75-l23 C-B; 14835; 164-114

